Analysis of the data from the study of the historical development of gene pools is completed, and these results will be prepared for publication. Study of cryptic variation at the XDH and ODH loci among linearly spaced close populations and more distant ones will continue with emphasis on distributions in samples from collections made at the same localities several years apart. New collections will be made along additional river systems to provide 1978 samples and several old sites will be recollected. Investigation of requirements for placing adult Drosophila in cold storage will concentrate on increased larval nutrition and cold treatment as preconditions to maximize longevity of adults stored at 3 degrees C. Cytological analysis will be used when necessary to expedite genetic analysis of newly discovered cryptic variation among electromorphs.